Oil/water separating devices of this type are frequently used in connection with air compressors. Air compressors produce compressed air by sucking in and compressing ambient air. In the process, the air humidity contained in the ambient air accumulates as a condensate due to physical reasons and due to the compressed air being dried. This condensate, being an oil/water mixture, is waste water which, owing to the content of lubricants, most frequently is not permitted to be discharged into the public sewer because it exceeds the hydrocarbon concentration limits.
Given a volume flow of 60 m3/h sucked-in air, a mostly discontinuous condensate flow of 1.23 l/h charged with 240 mg/h oil may typically be produced. This corresponds to 195 mg oil per liter of condensate. These values may fluctuate depending on various parameters, these parameters including, for example, climate conditions (ambient temperature and humidity), the type of oil used in the compressor and the construction and mode of operation of the compressor. The bond between water and the lubricant also varies and ranges from a mixture of oil and water to a dispersion and an emulsion. Admissible values for discharge into the sanitary sewer are, however, in the order of 10-20 mg/l, in part even 5 mg/l (oil/condensate). Thus, a special waste is produced which has to be disposed of by a waste disposal company, even though 99.5% percent of it is water from ambient air humidity.
For treating such a condensate, the use of oil/water separators is therefore known. In this case, the object of commercially available oil/water separators is to treat the condensate on-site so that it can be discharged, i.e. to remove the oil fractions from the water in a cost-effective manner. Known apparatuses of this design usually employ several separating stages in order to achieve the desired purity of the water. In the process, the condensate is typically discharged slowly, and thus with little turbulence, into a pre-separator via a pressure relief element. The former works according to the principle of gravity separation and provides for the deposition of heavy, sedimentary contaminants (density greater than 1 kg/dm3) and the floating of free oil fractions (density lower than 1 kg/dm3). These oil fractions then flow towards a collecting container. In a second stage, fine oil droplets are separated from the condensate by means of an adsorption filter, wherein the adsorption filters are frequently based on an oleophilic material and active carbon with a very large internal surface.
In another design according of the oil/water separator, the condensate, together with the free oil fractions, is fed through an adsorption filter, which in turn floats on the condensate surface and soaks up oil fractions that deposit here (density greater than 1 kg/dm3). Such an oil/water separator is known, for example, from DE 10 2006 009 542 A1. The design of this oil/water separator works according to the principle of corresponding water columns, wherein treated condensate leaves the apparatus at the pure-water outlet towards the sewer in the same amount as new condensate flows in.
In such oil/water separators, the collected free oils and the oil-saturated filters are usually thermally utilized, but may also be treated. Strongly dispersed or even emulsified condensates cannot be treated in these apparatuses and are usually treated by more complex methods, e.g. by diaphragm, evaporation or decomposition processes.
In operating such oil/water separators, there is often the problem that the flow resistance of the filters increases due to the saturation of the upper layers or due to a formation of biological slimy layers. In order to prevent overflowing or backwater, the filters must therefore be changed early, even though their capacity is not yet exhausted. To solve this problem, WO 2011/104 368 A1 proposes providing a mechanical separating device for separating slime-like substances and an electrical pump which sucks the condensate through the filter and thus overcomes flow resistance. This operation takes place if condensate is present, and is controlled through an electronic level detection means. In principle, the flow through the filter takes place only by means of the pump, which entails the aforementioned advantages but is accompanied by increased energy costs.